The present invention relates to an apparatus for detecting an abnormality of a motor and a method for detecting an abnormality of a motor.
A servo drive measures the amount of current flowing through a motor and controls the motor for accurate control. The measured value of the current is effective data representing the state of a motor, and the measured value of the current and an actual position of the motor are data for calculating the actual torque of the motor. A conventional apparatus for detecting an abnormality of a motor using the amount of current flowing through the motor is shown in FIG. 2.
The conventional abnormality detection apparatus includes an overcurrent detection apparatus and an overload detection apparatus. The overcurrent detection apparatus includes a current measurer 51 and an overcurrent detector 55. The current measurer 51 having a Hall sensor measures the current flowing through a motor 40 when a predetermined voltage is applied to the motor 40. The output of the current measurer 51 is input to the overcurrent detector 55. The overcurrent detector 55 judges whether the motor 40 has a malfunction when the input current corresponds to a value which departs from the boundary of normal operation of the motor 40.
The overload detection apparatus includes an encoder 61, an encoder signal processor 63 and an abnormality detector 70. The encoder 61 encodes the information about the current states of the motor 40 such as the position and speed of the motor 40, and transmits the encoded information. The encoder signal processor 63 outputs the position of the motor 40 based on the coded signal. The abnormality detector 70 calculates an actual torque of the motor 40 based on data for the position of the motor 40 input from the encoder signal processor 63 and a measured current value of the current measurer 51. The abnormality detector 70 has data corresponding to when the motor 40 operates normally. The data is compared with the calculated torque to discriminate whether an abnormality of the operation of the motor 40 exists.
If the overcurrent detector 55 or the overload detector 70 detects and abnormality of the motor 40, a controller (not shown) for controlling the motor 40 stops the operation of the motor 40 or takes actions necessary therefor.
The conventional abnormality detection apparatus detects an abnormality of the motor 40 assuming that the current value measured in the current measurer 51 is accurate. Thus, when the current measurement is in error, an abnormality of the motor may not be detected. Accordingly, when the current measurement system malfunctions due to, e.g., errors in the connection of the current measurer 51 and the defects of the current measurer 51, the motor 40 and a servo drive can be damaged.